We propose to examine the two Ni centers of carbon monoxide dehydrogenase enzyme from Clostridium thermoacticum independently using Ni and Co K-edge EXAFS. This study is made possible by the recent discovery that treatment of the enzyme with 1,10-phenanthroline removes the Ni from only one of the two NiFe centers. Previous EXAFS work on this enzyme has not led to a unique structural determination of the NiFe clusters because the two Ni sites are not spectroscopically distinguishable. We should be able to determine the structure of one site using Ni K-edge EXAFS of the phenanthroline treated enzyme, and the structure of the other site using Co K-edge EXAFS of the Co substituted phenanthroline treated enzyme.